In a conventional machine tool, it is known to use a feed device to move a workpiece holding portion relative to a spindle by driving at least one of the workpiece holding portion and the spindle by means of a drive unit. A typical feed device is configured with a guide mechanism for guiding a movable body and a drive mechanism for moving the movable body, and has a configuration in which operation of the drive mechanism is controlled by a controller.
As the guide mechanism, for example, a configuration comprising a slide guide mechanism or a rolling guide mechanism is given, and as the drive mechanism, a configuration comprising a ball screw, a nut screwed onto the ball screw and fixedly provided on the movable body, and a drive motor for rotating the ball screw about an axis thereof to move the movable body in the direction of the axis of the ball screw is given.
The controller generates a control signal on the basis of a target moving position of the movable body and transmits a drive current based on the generated control signal to the drive motor, thereby driving the drive motor. Thereby, the ball screw is rotated about the axis thereof and the movable body is moved to the target moving position.
In a machine tool, a very high machining accuracy is generally required, and therefore various techniques to correct a feeding position error, such as a position error correction method as described in the patent document 1, for example, are used. The patent document 1 discloses a method of correcting a position error for a case where three axes are not strictly perpendicular to one another due to a manufacturing error or the like and there is a squareness error between each axis. In a conventional machine tool, such a correction technique is used to correct a feeding position error, thereby achieving a highly accurate machining.